We encountered a rare case of neurohypophyseal germinoma with a prominent granulomatous reaction, which invaded the right cavernous sinus. The neuroimaging and histopathology features in this case were unique, distinguishing it from other types of suprasellar lesions. A 13-year-old boy presented with loss of appetite and polyuria; both symptoms were present for 1 year, and headache, general fatigue and blurred vision present for the prior 2 months. On admission, neurological examination indicated bitemporal hemianopsia and optic atrophy. Endocrinological exam showed panhypopituitarism. Tumor markers such as alpha-fetoprotein, human growth hormone, carcinoembryonic antigen, and placental alkaline phosphatase were negative. Brain CT revealed a suprasellar tumor with calcification. MR T(1)-weighted and T(2)-weighted images showed the tumor to be isointense to normal brain parenchyma and to be enhanced densely. The tumor also involved the right cavernous sinus, so that a biopsy was performed by the transsphenoidal approach. On pathologic examination of the specimen, typical large tumor cells with lymphocytic cell infiltration and prominent granulomatous reaction were observed. Neurohypophyseal granulomatous germinoma was diagnosed. Radiotherapy was performed with a total dose of 51 Gy and the tumor shrank remarkably. The patient returned to school under hormone replacement therapy.